The fabrication of self-supporting films of electron emissive materials suspended in a binder is well known and is discussed in U.S. Pat. No. 2,974,364 assigned to the Assignee of the present application. It is also well known that such self-supporting films are readily cut to size and affixed to a cathode support member to provide a cathode structure. Such procedures are set forth and discussed in U.S. Pat. Nos. 2,986,671 and 3,223,569 for example.
Further, it is known that cathodes for cathode ray tubes may be fabricated by a process wherein a cathode support member is wetted with a thin layer of solvent for the binder of a self-supporting film of emissive materials. Then, a circle or some other configuration is stamped or cut out of the self-supporting film and placed in contact with the solvent wetted cathode support member. Thereupon, the solvent is evaporated, the film is slightly dissolved by the solvent at the interface surface and affixed to the cathode support member to provide a cathode for a cathode ray tube.
Although the above-described process has been and still is employed with varying results, it has been found that serious deficiencies exist in the above-described and known techniques. More specifically, it has been found that centering of the films on the cathode support member, adherence of the film to the support member, and densification of the film by the solvent are all problems encountered in fabricating cathodes for cathode ray tubes.
For example, one known cathode fabricating technique provides for wetting of the cathode support member with a solvent for the binder of the self-supporting film. However, it has been found that it is most difficult to provide a uniform and consistent layer of solvent on the support member. As a result, incomplete coverage by the solvent causes poor adherence of the film with the edges of the film tending to lift from the support member.
On the other hand, if an excess of solvent is present on the cathode support member the solvent dissolves too much of the film and, upon drying, densification of selected parts of the film are encountered. As a result, the electron emissive capabilities of the cathode are deleteriously affected.
Also, one known technique for fabricating cathodes for cathode ray tubes provides for stamping a film circle from a larger film strip and blowing the stamped film circle onto a solvent wetted cathode support member. However, it has been found that it is impractical, if not nearly impossible, to blow the film circle in a manner to achieve repetitive landing thereof in an exact location such as the center of the cathode support member.
More specifically, it has been found that a thin layer of solvent on the cathode support member does not provide the buoyancy and surface tension necessary to "float" the film circle. Thus, the film circle remains at the landing location and is often undesirably not centered on the support member. Obviously, such conditions are undesirable and do not provide uniform cathodes or uniform cathode ray tubes.